PROJECT SUMMARY/ABSTRACT Opioid use disorder (OUD) and mortality from opioid overdose are significant public health concerns. Deaths from opioid overdose are highly preventable with early detection and administration of naloxone. A key challenge of the epidemic is that overdose victims often die because they are alone or among untrained or impaired bystanders and thus do not receive timely resuscitation. There is an urgent, unmet need for a low-barrier, easily scalable solution that can identify opioid overdoses in real-time and rapidly connect victims to naloxone therapy. The goal of Sound Life Sciences? (SLS) Fast-Track proposal is to commercialize an innovative overdose detection software product that can be downloaded on any commodity smartphone and can detect opioid- induced respiratory failure (i.e., overdose) and summon help. The software-only product, SecondChance, converts a smartphone into a short-range active sonar system capable of monitoring breathing and detecting overdose. SecondChance requires no additional hardware and leverages the native speaker/microphone array inside the phone and proprietary overdose detection signal processing algorithms. The software enables an individual to monitor themselves when they are at risk for an overdose and, in the event of an overdose, SecondChance can summon help, either from a friend or family member or from emergency medical services (EMS). Sound Life Sciences? long-term goal is to keep individuals with OUD safe until they are able to access treatment and achieve durable recovery. In Phase I of this Fast-Track application, SLS will convert the SecondChance prototype (for which feasibility has been established) into a minimum viable product (MVP) based on rapid iteration guided by feedback and usability testing. In Phase II, using human factors engineering approaches, SLS will complete the SecondChance System and systematically validate each component: the patient monitoring app, the HIPAA-compliant data collection and storage infrastructure, and the emergency services integration. The Phase II studies will culminate in a 510(k) submission to the FDA. The SecondChance System will be marketed to naloxone manufacturers, local governments and people with OUD to ensure rapid dissemination to at-risk individuals. Given the number of people with OUD and costs associated with opioid overdose, there is a substantial market for the SecondChance System.